1. Field of the Invention
The present invention relates to a tuner, a digital demodulating apparatus, a controlling method of the apparatus, a computer program product for the apparatus, a recording medium recording thereon the product, and a digital receiver.
2. Description of Related Art
In a tuner that performs channel select processing to a signal received through an antenna or the like, an output signal from a circuit element constituting the tuner contains various kinds of noises. The noises contained in the output signal from the circuit element includes noise caused by an interfering wave that has been mixed in the signal when the signal is received by the antenna or the like; and noise caused by thermal noise of the circuit element. On the other hand, a change in electric power supplied to the circuit element brings about changes in intensity of the noises. For example, when the power supplied to the circuit element decreases, in general, the noise caused by the interfering wave increases rapidly. Too much increase in the noise brings about an inconvenience that information contained in the received signal can not accurately be obtained. Therefore, when such an interfering wave exists, electric power of an intensity more than that when no interfering wave exists must be supplied to the circuit element in order to suppress the intensity of the noise.
JP-A-2001-292037 discloses a technique in which supply of electric power to a circuit element is controlled synchronously with timings at which signals are transmitted from a portable mobile phone device. When the device transmits a signal, the signal is received by an antenna of the device itself. Thus, when a signal is transmitted, the transmitted signal is mixed in a received signal as an interfering wave. According to the technique of JP-A-2001-292037, when the device is transmitting a signal, the circuit element is supplied with electric power of an intensity in the degree that the noise caused by the transmitted signal brings about no inconvenience. Contrastingly, when the device is transmitting no signal, the circuit element is supplied with electric power of an intensity less than that when the device is transmitting a signal. Thereby, the intensity of noise to be mixed in the output signal from the circuit element due to the interfering wave can be suppressed, and the power consumption of the circuit element can be suppressed.
However, the intensity of noise caused by an interfering wave also depends on the intensity of the interfering wave. Therefore, the control according to JP-A-2001-292037 can be effective only when it can be estimated what degree of intensity of the interfering wave is mixed in the received signal. On the other hand, mixing an interfering wave in a received signal occurs not only when the device itself transmits a signal. For example, a signal transmitted another device near the device in question may be mixed in a received signal as an interfering wave. That is, it is impossible to always accurately estimate what degree of intensity of the interfering wave to be mixed. Therefore, in order that noise caused by any interfering wave is prevented from bringing about inconvenience, the circuit element must be always supplied with electric power of an intensity more than that required when any interfering wave does not exist. However, the intensity of electric power required for preventing inconvenience caused by any interfering wave is considerably large. This brings about too much increase in the power consumption of the tuner.
Therefore, it is important that the intensity of electric power to be supplied is controlled in accordance with reception conditions so that signal reception is made possible under various reception conditions, such as existence of an interfering wave, and the intensity of electric power to be supplied does not increase more than necessity.